Potassium chromate. Production, chemical and physical properties. Application

Potassium chromate or potassium chromate (international names: Kalium chromicum, Kaliumchromat, Potassium chromate) is an inorganic compound, yellow crystals of the rhombic system, soluble in water. Refers to salts of chromic acid H2CrO4, which does not exist in the free state. The substance potassium chromate has the following formula: CrK2O4

How to get potassium chromate?

Potassium chromate is obtained in several ways:

1. By oxidizing potassium chromium oxide with chlorate (the reaction occurs at a temperature of 500-700 degrees): Cr2O3 (chromium oxide) + KClO3 (potassium chlorate) + K2CO3 (potassium carbonate) = 2K2CrO4 (potassium chromate) + KCl (potassium chloride) + 2CO2 (carbon dioxide gas)
2. By dissolving chromium oxide in potassium hydroxide: CrO3 (chromium oxide) + 2KOH (potassium hydroxide) = K2CrO4 (potassium chromate) + H2O (water)
3. By decomposition of potassium dichromate when it is heated (the reaction is carried out at a temperature of 500-600 degrees): 4K2Cr2O7 (potassium dichromate) = 4K2CrO4 (potassium chromate) + 2Cr2O3 (chromium oxide) + 3O2 (oxygen)
4. By applying a concentrated solution of potassium hydroxide to potassium dichromate: K2Cr2O7 (potassium dichromate) + 2KOH (potassium hydroxide) = 2K2CrO4 (potassium chromate) + H2O (water)
5. A rare mineral called tarapakait is rarely found in nature. This is potassium chromate with impurities.

Chemical properties of potassium chromate:

1. In dilute acids, potassium chromate transfers to potassium dichromate, the formula of which is K2Cr2O7. An example is the following reaction: 2K2CrO4 (potassium chromate) + 2HCl ( diluted hydrochloric acid ) = K2Cr2O7 (potassium dichromate) + 2KCl (potassium chloride) + H2O (water).
2. When interacting with concentrated acids, another reaction already takes place, for example: K2CrO4 (potassium chromate) + 2HCl (hydrochloric acid in concentrated form) = K (Cr (Cl) O3) (complex chromium compound) + KCl (potassium chloride) + H2O (water )
3. When interacting with hot concentrated potassium acids, chromate exhibits oxidative properties. An example is the following reaction carried out at a temperature of 90 degrees: 2K2CrO4 (potassium chromate) + 16HCl (hydrochloric acid) = 2CrCl3 (chromium chloride) + 3Cl2 (chlorine as a gas) + 4KCl (potassium chloride) + 8H2O (water).
4. Potassium chromate can enter into metabolic reactions. For example: K2CrO4 (potassium chromate) + 2AgNO3 (silver nitrate) = Ag2CrO4 (silver chromate, precipitated) + 2KNO3 (potassium nitrate); K2CrO4 (potassium chromate) + Hg2 (NO3) 2 (mercury nitrate) = Hg2CrO4 (mercury chromate, precipitated) + 2KNO3 (potassium nitrate).

Physical properties of potassium chromate:

1. The density is 2.732 g / cm3.
2. Potassium chromate melts at a temperature of 968.3 ° C. At a temperature of 668 degrees, it goes into the red hexagonal phase - takes on a different color - red. However, upon cooling, it again turns yellow.
3. Forms yellow crystals of the rhombic system.
4. Belongs to the space group P-nam.
5. Refers to paramagnets.
6. It is poorly soluble in ethanol, soluble in water. Insoluble in ethyl and diethyl alcohol.
7. The molar mass is 194.19 g / mol.

Optical properties of potassium chromate

The refractive index is 1.74.

Where is potassium chromate used?

1. In the leather industry it is used as a tanning agent. When dyeing fabrics, it is used as a mordant.
2. It is used as one of the components of the composition of electrolytes of special chemical degreasing.
3. As a bleach for wax and oil.
4. In organic synthesis as an oxidizing agent, for example, in the manufacture of dyes.
5. Potassium chromate is also used for the preparation of electrochemical silver oxidation solution and for the passivation of products from copper and silver alloys.
6. It is used in medicine as a homeopathic remedy.
7. In laboratories for washing dishes, a mixture of equal volumes of concentrated sulfuric acid and a solution of K2Cr2O7, pre-saturated in the cold, is used.

Potassium Dichromate (technical name - chrompeak)

Represents crystals of red-orange color. It does not form crystalline hydrates, has a density of 2.684 grams per cubic centimeter, and melts at a temperature of 397 degrees. With further heating, it decomposes. The solubility in water at 20 degrees is 12.48 grams of salt per 100 grams of water. Potassium dichromate has been widely used as an oxidizing agent in pyrotechnics, match industry and in chromametry as a reagent.